Demo entry 6746667

#!/bin/bash############################################################################### SHORTCUTS##############################################################################
CTRL+A # move to beginning of line
CTRL+B # moves backward one character
CTRL+C # halts the current command
CTRL+D # deletes one character backward or logs out of current session, similar to exit
CTRL+E # moves to end of line
CTRL+F # moves forward one character
CTRL+G # aborts the current editing command and ring the terminal bell
CTRL+J # same as RETURN
CTRL+K # deletes (kill) forward to end of line
CTRL+L # clears screen and redisplay the line
CTRL+M # same as RETURN
CTRL+N # next line in command history
CTRL+O # same as RETURN, then displays next line in history file
CTRL+P # previous line in command history
CTRL+R # searches backward
CTRL+S # searches forward
CTRL+T # transposes two characters
CTRL+U # kills backward from point to the beginning of line
CTRL+V # makes the next character typed verbatim
CTRL+W # kills the word behind the cursor
CTRL+X # lists the possible filename completions of the current word
CTRL+Y # retrieves (yank) last item killed
CTRL+Z # stops the current command, resume with fg in the foreground or bg in the background
ALT+B # moves backward one word
ALT+D # deletes next word
ALT+F # moves forward one word
DELETE # deletes one character backward
!! # repeats the last commandexit# logs out of current session############################################################################### BASH BASICS##############################################################################
env # displays all environment variablesecho$SHELL# displays the shell you're usingecho$BASH_VERSION# displays bash version
bash # if you want to use bash (type exit to go back to your previously opened shell)
whereis bash # finds out where bash is on your system
which bash # finds out which program is executed as 'bash' (default: /bin/bash, can change across environments)
clear # clears content on window (hide displayed lines)############################################################################### FILE COMMANDS##############################################################################
ls # lists your files in current directory, ls <dir> to print files in a specific directory
ls -l # lists your files in 'long format', which contains the exact size of the file, who owns the file and who has the right to look at it, and when it was last modified
ls -a # lists all files, including hidden files (name beginning with '.')
ln -s <filename> <link> # creates symbolic link to file
touch <filename> # creates or updates (edit) your file
cat <filename> # prints file raw content (will not be interpreted)
any_command > <filename> # '>' is used to perform redirections, it will set any_command's stdout to file instead of "real stdout" (generally /dev/stdout)
more <filename> # shows the first part of a file (move with space and type q to quit)
head <filename> # outputs the first lines of file (default: 10 lines)
tail <filename> # outputs the last lines of file (useful with -f option) (default: 10 lines)
vim <filename> # opens a file in VIM (VI iMproved) text editor, will create it if it doesn't exist
mv <filename1> <dest> # moves a file to destination, behavior will change based on 'dest' type (dir: file is placed into dir; file: file will replace dest (tip: useful for renaming))
cp <filename1> <dest> # copies a file
rm <filename> # removes a file
diff <filename1> <filename2> # compares files, and shows where they differ
wc <filename> # tells you how many lines, words and characters there are in a file. Use -lwc (lines, word, character) to ouput only 1 of those informations
chmod -options <filename> # lets you change the read, write, and execute permissions on your files (more infos: SUID, GUID)
gzip <filename> # compresses files using gzip algorithm
gunzip <filename> # uncompresses files compressed by gzip
gzcat <filename> # lets you look at gzipped file without actually having to gunzip it
lpr <filename> # prints the file
lpq # checks out the printer queue
lprm <jobnumber> # removes something from the printer queue
genscript # converts plain text files into postscript for printing and gives you some options for formatting
dvips <filename> # prints .dvi files (i.e. files produced by LaTeX)
grep <pattern> <filenames> # looks for the string in the files
grep -r <pattern> <dir> # search recursively for pattern in directory############################################################################### DIRECTORY COMMANDS##############################################################################
mkdir <dirname> # makes a new directorycd# changes to homecd <dirname> # changes directorypwd# tells you where you currently are############################################################################### SSH, SYSTEM INFO & NETWORK COMMANDS##############################################################################
ssh user@host # connects to host as user
ssh -p <port> user@host # connects to host on specified port as user
ssh-copy-id user@host # adds your ssh key to host for user to enable a keyed or passwordless login
whoami # returns your username
passwd # lets you change your password
quota -v # shows what your disk quota is
date # shows the current date and time
cal # shows the month's calendar
uptime # shows current uptime
w # displays whois online
finger <user> # displays information about user
uname -a # shows kernel information
man <command> # shows the manual for specified command
df # shows disk usage
du <filename> # shows the disk usage of the files and directories in filename (du -s give only a total)
last <yourUsername> # lists your last logins
ps -u yourusername # lists your processeskill <PID> # kills the processes with the ID you gave
killall <processname> # kill all processes with the name
top # displays your currently active processesbg# lists stopped or background jobs ; resume a stopped job in the backgroundfg# brings the most recent job in the foregroundfg <job> # brings job to the foreground
ping <host> # pings host and outputs results
whois <domain> # gets whois information for domain
dig <domain> # gets DNS information for domain
dig -x <host> # reverses lookup host
wget <file> # downloads file############################################################################### VARIABLES##############################################################################varname=value # defines a variablevarname=value command# defines a variable to be in the environment of a particular subprocessecho$varname# checks a variable's valueecho$$# prints process ID of the current shellecho$!# prints process ID of the most recently invoked background jobecho$?# displays the exit status of the last commandexportVARNAME=value # defines an environment variable (will be available in subprocesses)
array[0]=valA # how to define an array
array[1]=valB
array[2]=valC
array=([2]=valC [0]=valA [1]=valB)# another wayarray=(valA valB valC)# and another${array[i]}# displays array's value for this index. If no index is supplied, array element 0 is assumed${#array[i]}# to find out the length of any element in the array${#array[@]}# to find out how many values there are in the arraydeclare -a # the variables are treaded as arraysdeclare -f # uses function names onlydeclare -F # displays function names without definitionsdeclare -i # the variables are treaded as integersdeclare -r # makes the variables read-onlydeclare -x # marks the variables for export via the environment${varname:-word}# if varname exists and isn't null, return its value; otherwise return word${varname:=word}# if varname exists and isn't null, return its value; otherwise set it word and then return its value${varname:?message}# if varname exists and isn't null, return its value; otherwise print varname, followed by message and abort the current command or script${varname:+word}# if varname exists and isn't null, return word; otherwise return null${varname:offset:length}# performs substring expansion. It returns the substring of $varname starting at offset and up to length characters${variable#pattern}# if the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest${variable##pattern}# if the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest${variable%pattern}# if the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest${variable%%pattern}# if the pattern matches the end of the variable's value, delete the longest part that matches and return the rest${variable/pattern/string}# the longest match to pattern in variable is replaced by string. Only the first match is replaced${variable//pattern/string}# the longest match to pattern in variable is replaced by string. All matches are replaced${#varname}# returns the length of the value of the variable as a character string
*(patternlist)# matches zero or more occurrences of the given patterns
+(patternlist)# matches one or more occurrences of the given patterns
?(patternlist)# matches zero or one occurrence of the given patterns
@(patternlist)# matches exactly one of the given patterns
!(patternlist)# matches anything except one of the given patterns$(UNIX command)# command substitution: runs the command and returns standard output############################################################################### FUNCTIONS############################################################################### The function refers to passed arguments by position (as if they were positional parameters), that is, $1, $2, and so forth.# $@ is equal to "$1" "$2"... "$N", where N is the number of positional parameters. $# holds the number of positional parameters.function functname(){
shell commands
}unset -f functname # deletes a function definitiondeclare -f # displays all defined functions in your login session############################################################################### FLOW CONTROLS##############################################################################
statement1 && statement2 # and operator
statement1 || statement2 # or operator
-a # and operator inside a test conditional expression
-o # or operator inside a test conditional expression# STRINGSstr1= str2 # str1 matches str2
str1 != str2 # str1 does not match str2
str1 < str2 # str1 is less than str2 (alphabetically)
str1 > str2 # str1 is greater than str2 (alphabetically)
-n str1 # str1 is not null (has length greater than 0)
-z str1 # str1 is null (has length 0)# FILES
-a file # file exists
-d file # file exists and is a directory
-e file # file exists; same -a
-f file # file exists and is a regular file (i.e., not a directory or other special type of file)
-r file # you have read permission
-r file # file exists and is not empty
-w file # your have write permission
-x file # you have execute permission on file, or directory search permission if it is a directory
-N file # file was modified since it was last read
-O file # you own file
-G file # file's group ID matches yours (or one of yours, if you are in multiple groups)
file1 -nt file2 # file1 is newer than file2
file1 -ot file2 # file1 is older than file2# NUMBERS
-lt # less than
-le # less than or equal
-eq # equal
-ge # greater than or equal
-gt # greater than
-ne # not equalif condition
then
statements
[elif condition
then statements...][else
statements]fifor x in {1..10}do
statements
donefor name [in list]do
statements that can use $namedonefor(( initialisation ; ending condition ; update ))do
statements...
donecase expression in
pattern1 )
statements ;;
pattern2 )
statements ;;esacselect name [in list]do
statements that can use $namedonewhile condition;do
statements
doneuntil condition;do
statements
done############################################################################### COMMAND-LINE PROCESSING CYCLE############################################################################### The default order for command lookup is functions, followed by built-ins, with scripts and executables last.# There are three built-ins that you can use to override this order: `command`, `builtin` and `enable`.command# removes alias and function lookup. Only built-ins and commands found in the search path are executedbuiltin# looks up only built-in commands, ignoring functions and commands found in PATHenable# enables and disables shell built-inseval# takes arguments and run them through the command-line processing steps all over again############################################################################### INPUT/OUTPUT REDIRECTORS##############################################################################
cmd1|cmd2 # pipe; takes standard output of cmd1 as standard input to cmd2
< file # takes standard input from file
> file # directs standard output to file
>> file # directs standard output to file; append to file if it already exists
>|file # forces standard output to file even if noclobber is set
n>|file # forces output to file from file descriptor n even if noclobber is set
<> file # uses file as both standard input and standard output
n<>file # uses file as both input and output for file descriptor n
n>file # directs file descriptor n to file
n<file # takes file descriptor n from file
n>>file # directs file description n to file; append to file if it already exists
n>&# duplicates standard output to file descriptor n
n<&# duplicates standard input from file descriptor n
n>&m # file descriptor n is made to be a copy of the output file descriptor
n<&m # file descriptor n is made to be a copy of the input file descriptor&>file # directs standard output and standard error to file
<&- # closes the standard input
>&- # closes the standard output
n>&- # closes the ouput from file descriptor n
n<&- # closes the input from file descripor n############################################################################### PROCESS HANDLING############################################################################### To suspend a job, type CTRL+Z while it is running. You can also suspend a job with CTRL+Y.# This is slightly different from CTRL+Z in that the process is only stopped when it attempts to read input from terminal.# Of course, to interrupt a job, type CTRL+C.
myCommand &# runs job in the background and prompts back the shelljobs# lists all jobs (use with -l to see associated PID)fg# brings a background job into the foregroundfg %+ # brings most recently invoked background jobfg %- # brings second most recently invoked background jobfg %N # brings job number Nfg %string # brings job whose command begins with stringfg %?string # brings job whose command contains stringkill -l # returns a list of all signals on the system, by name and numberkill PID # terminates process with specified PID
ps # prints a line of information about the current running login shell and any processes running under it
ps -a # selects all processes with a tty except session leaderstrap cmd sig1 sig2 # executes a command when a signal is received by the scripttrap"" sig1 sig2 # ignores that signalstrap - sig1 sig2 # resets the action taken when the signal is received to the defaultdisown <PID|JID> # removes the process from the list of jobswait# waits until all background jobs have finished############################################################################### TIPS & TRICKS############################################################################### set an alias
cd; nano .bash_profile
> aliasgentlenode='ssh admin@gentlenode.com -p 3404'# add your alias in .bash_profile# to quickly go to a specific directory
cd; nano .bashrc
> shopt -s cdable_vars
> exportwebsites="/Users/mac/Documents/websites"source .bashrc
cd$websites############################################################################### DEBUGGING SHELL PROGRAMS##############################################################################
bash -n scriptname # don't run commands; check for syntax errors onlyset -o noexec # alternative (set option in script)
bash -v scriptname # echo commands before running themset -o verbose # alternative (set option in script)
bash -x scriptname # echo commands after command-line processingset -o xtrace # alternative (set option in script)trap'echo $varname' EXIT # useful when you want to print out the values of variables at the point that your script exitsfunction errtrap {es=$?echo"ERROR line $1: Command exited with status $es."}trap'errtrap $LINENO' ERR # is run whenever a command in the surrounding script or function exits with non-zero status function dbgtrap {echo"badvar is $badvar"}trap dbgtrap DEBUG # causes the trap code to be executed before every statement in a function or script# ...section of code in which the problem occurs...trap - DEBUG # turn off the DEBUG trapfunction returntrap {echo"A return occurred"}trap returntrap RETURN # is executed each time a shell function or a script executed with the . or source commands finishes executing